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Applications that require the measurement of various physical quantities are known in the art. Some measurements commonly made are temperature, pressure, and dimensions such as thickness and distance. The systems that make such measurements generally consist of two subsystems: one or more sensors and a signal-processing unit in electrical communication with the one or more sensors. It is quite common for sensors to need field replacement. To avoid the necessity for complex recalibration procedures that may require specialized equipment and techniques when replacing such sensors, various schemes have been employed. Typically, sensors are factory-normalized so their output conforms to a particular function. When sensors so normalized are connected to signal-processing units that are also factory normalized to expect the particular sensor function, an output of some desired accuracy can be obtained.
In order to normalize sensor outputs, several techniques have been employed; the sensor may be physically adjusted (e.g., laser-trimmed) or have electronic components selected or adjusted. The sensor may contain circuitry for informing the signal-processing unit about its transfer function. For example, it may do so by way of nonvolatile digital memory. Other techniques not specifically mentioned here may be employed.
A disadvantage of such methods is that they require both the sensor and the signal-processing unit to be normalized, or, if the sensor contains circuitry to describe its transfer function to the signal-processing unit, this circuitry must be installed and the signal-processing unit still must be normalized. These methods add cost to the sensor and the signal-processing unit, and may, in addition, add size, weight, or other undesirable constraints upon the sensor design.
A method for facilitating field replacement of sensors is presented. The replacement sensor""s transfer function need only be measured, not adjusted, and the signal-processing unit""s transfer function need only be adjusted, but not measured, to achieve simple field-replacement of sensors. With this method simple calculations and adjustments, typically expedited by means of a computer program, can be made in the field when sensor replacement is required. By way of the presently disclosed method sensor cost and size are not increased since no normalization techniques or components are required.